Check if closing a gtk window/dialog creates no artifacts both on xorg and on wayland.

Original Bug Report
===================
The Ubuntu Error Tracker has been receiving reports about a problem regarding gnome-control-center. This problem was most recently seen with package version 1:3.26.0-0ubuntu3, the problem page at https://errors.ubuntu.com/problem/f738a467f5d04cbf9ac6cf7554a28bd064e4091a contains more details, including versions of packages affected, stacktrace or traceback, and individual crash reports.
If you do not have access to the Ubuntu Error Tracker and are a software developer, you can request it at http://forms.canonical.com/reports/.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-artful to verification-done-artful. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-artful. In either case, details of your testing will help us make a better decision.

The verification of the Stable Release Update for gtk+3.0 has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.